This proposal represents a multi-disciplinary approach to develop an envelope-containing heat-treated pseudovirion vaccine using novel applications of classical viral vaccine technologies. Our overall hypothesis is that an envelope-containing heat-treated pseudovirion could serve as the basis for a safe and effective HIV vaccine. Data from ongoing vaccine trials indicate that a preventive HIV vaccine is going to need to elicit broad-based immune responses. DNA and vector-based vaccines have been successful at inducing T cell responses, but these appear to be insufficient to provide protection from infection. Relevant neutralizing antibodies can offer protection from infection if they are present in sufficient concentrations at the time of infection. Unfortunately, attempts to induce potent neutralizing antibody responses with recombinant monomeric subunit vaccines have generally been unsuccessful. This limited success suggests that a vaccine will likely need to mimic or improve upon the native envelope structure. Taken together, it is crucial to explore vaccine strategies capable of eliciting potent antibody responses to be used alone, or in conjunction with vaccines that target cellular responses. The use of whole virions provides a complex antigen with close to native conformation and is one approach which could be taken to develop a safe and effective HIV-1 vaccine. An envelope-containing heat-treated pseudovirion has a theoretical advantage over a whole killed vaccine since it would consist of a complex mixture of immunogenic viral antigens, but could be engineered to be defective in regions important for infectivity, as well as in regions that serve as potential decoys for potent immune responses. More importantly, we have developed procedures which result in enhanced antigenicity of oligomeric envelope structures on whole virions which can be easily adapted to envelope-containing pseudovirions. Our Specific Aims are: Aim 1: To test the hypothesis that an envelope-containing pseudovirion will demonstrate enhanced antigenicity following heat treatment in a manner analogous to a heat-treated whole virion. Aim 2: To test the hypothesis that vaccination with an envelope-containing heat-treated pseudovirion can result in the induction of potent neutralizing antibodies in a small animal model. Aim 3: To test the hypothesis that vaccination with an envelope-containing heat-treated pseudovirion can result in the induction of humoral and cellular immune responses generally regarded as protective in non human primates. Aim 4: To test the hypothesis that an envelope-containing heat-treated pseudovirion can protect rhesus macaques against infection with a heterologous SHIV.